Abstract In order to study the performance, cycling stability and safety of electrochemical storage devices, various characterisation methods are applied. Magic angle spinning (MAS) NMR enables ex situ studies of electrochemical reactions with high resolution. In the present work, we follow the changes that occur in the MAS NMR spectra of lithiated graphitic materials after storage. The measuring time has been significantly shortened by using fine-grained graphitic material with 65% 13C-isotope enrichment. Our results show that for 13C graphitic electrode material with a low lithiation degree, visible changes in the 13C NMR spectra are observed already in few hours, whereas the samples with a higher lithiation degree demonstrated greater stability even after several days. We analyzed the deintercalation behavior in these materials using 7Li MAS NMR and oxidation processes using in situ X-ray photoelectron spectroscopy. During storage Li ions migrate to the other interlayers (redistribution), large pores and to the surface, where interaction with air takes place. Effects of charge transfer from Li to graphite across four graphitic layers guarantees that 13C NMR spectra are less affected by these effects. The key finding is that special care has to be paid to the ex situ characterisation of electrochemically prepared graphitized materials.

中文翻译：

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锂插层细晶石墨材料的稳定性

摘要 为了研究电化学存储装置的性能、循环稳定性和安全性，应用了多种表征方法。魔角旋转 (MAS) NMR 能够以高分辨率对电化学反应进行非原位研究。在目前的工作中，我们跟踪了锂化石墨材料在储存后的 MAS 核磁共振谱中发生的变化。通过使用具有 65% 13C 同位素富集的细粒石墨材料，测量时间已显着缩短。我们的结果表明，对于具有低锂化度的 13C 石墨电极材料，在几个小时内就可以观察到 13C NMR 光谱的可见变化，而具有较高锂化度的样品即使在几天后也表现出更大的稳定性。我们使用 7Li MAS NMR 和使用原位 X 射线光电子能谱的氧化过程分析了这些材料的脱嵌行为。在储存过程中，锂离子迁移到其他夹层（重新分布）、大孔和表面，在那里与空气发生相互作用。跨越四个石墨层从锂到石墨的电荷转移效应保证了 13C NMR 光谱受这些效应的影响较小。关键发现是必须特别注意电化学制备的石墨化材料的非原位表征。跨越四个石墨层从锂到石墨的电荷转移效应保证了 13C NMR 光谱受这些效应的影响较小。关键发现是必须特别注意电化学制备的石墨化材料的非原位表征。跨越四个石墨层从锂到石墨的电荷转移效应保证了 13C NMR 光谱受这些效应的影响较小。关键发现是必须特别注意电化学制备的石墨化材料的非原位表征。